LP85571 datasheet(20/49 Pages) TI2

20 / 49 page

LP8557, LP85571

SNVSA15B – DECEMBER 2013 – REVISED DECEMBER 2015

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Feature Description (continued)

8.3.6.4 Thermal Shutdown

If the internal temperature reaches 150°C, the deviceimmediately shuts down the backlight to protect it from

damage. The TSD bit is also set in the STATUS register. The device re-activates the backlight again when the

internal temperature drops below 130°C.

8.3.6.5 Boost Overcurrent Protection

The device automatically limits boost current to 2.4 A . When the 2.4-A limit is reached the BST_OCP bit is set in

the STATUS register. It is normal for the device to trigger the boost current limit during the start-up or sudden

brightness changes. The STATUS register can be cleared by reading the bit. If the bit is permanently set, it may

indicate an issue in the application.

8.3.6.6 Boost Overvoltage Protection

The device automatically limits boost voltage to VBOOST_MAX + 1.6 V. When the limit is reached the BST_OVP

bit is set in the STATUS register. It is normal for the device to trigger the boost OVP limit during the start-up or

sudden brightness changes. The status register can be cleared by reading the bit. If the bit is permanently set, it

may indicate an issue in the application.

8.3.6.7 Boost Undervoltage Protection

The device can detect when the boost voltage is below VBOOST – 2.5 V for longer than 6 ms. When the

threshold is reached the BST_UV bit is set in the STATUS register.

8.4 Device Functional Modes

8.4.1 Shutdown Mode

The device is in shutdown mode when the VDD pin is low. Current consumption in this mode from VDD pin is

< 1 µA.

8.4.2 Active Mode

In active mode the backlight is enabled either with setting the ON register bit high (LP8557I) or by activating

PWM input (LP8557). The power supplying the VDD pin must be present. Brightness is controlled with I2C writes

to brightness registers or by changing PWM input duty cycle (operation without I2C control). Configuration

registers are not accessible in Active mode to prevent damage to the device by accidental writes. Current

consumption from VDD terminal in this mode is typically 2.2 mA when LEDs are not drawing any current.

8.5 Programming

8.5.1 I2C-Compatible Serial Bus Interface

8.5.1.1 Interface Bus Overview

The I2C-compatible synchronous serial interface provides access to the programmable functions and registers on

the device. This protocol uses a two-wire interface for bi-directional communications between the devices

connected to the bus. The two interface lines are the serial data line (SDA), and the serial clock line (SCL).

These lines must be connected to a positive supply, via a pull-up resistor and remain HIGH even when the bus is

idle.

The default 7-bit I2C address for the LP8557I slave is 2Ch.

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